Clear rectangle processing

ABSTRACT

High definition media content processing techniques are described in which enhanced media content rendering techniques may be performed to output high definition media content. In an implementation, luma keying may be provided to define clear pixels in a composite output using an optimum set of graphics processing instructions. In another implementation, techniques are described which may provide clear rectangles in a composite output of one or more video streams. Clear rectangles to appear in the composite output are configured by a media playback application. A texture is arrived at to represent a union of each of the clear rectangles and is applied to form the clear rectangles in the composite output. In another implementation, capture techniques are described in which an image to capture is resolved as strips to an intermediate texture and then from the texture to a capture buffer in system memory.

PRIORITY

This application is a continuation of and claims priority under 35U.S.C. §120 to application Ser. No. 11/935,519 filed on Nov. 6, 2007 andtitled “High Definition Media Content Processing,” the disclosure ofwhich is incorporated by reference herein in its entirety.

BACKGROUND

Options that are available to users for media content are everincreasing. For example, more and more media content is available inhigh definition resolutions. Devices such as televisions and opticaldisk playback devices supporting high definition media content areincreasingly in demand.

However, traditional techniques to render media content on such devicesmay not be suitable for high definition media content due to increasedprocessing demands to handle the higher resolution. For example, eachframe of high definition video content may contain over two millionindividual pixels to process for output. Thus, traditional techniquesdeveloped to handle fewer pixels may overburden processing resourceswhen applied to processing of high definition media content. This mayresult in a variety of detrimental effects which detract from the userexperience, such as slow processing, “choppy” playback, incorrect orincomplete processing and so forth.

SUMMARY

High definition media content processing techniques are described inwhich a one or more modules may perform enhanced rendering techniques tooutput high definition and/or other media content. In an implementation,luma keying is provided using an optimum set of graphics processinginstructions. Luma keying may be performed on a pixel-by-pixel basis tocause select pixels of a composite output to appear transparent. Foreach pixel, a maximum value is arrived at as the greater of a pixel'sluma value minus a high threshold value and a low threshold value minusthe pixel's luma value. When the maximum value for a respective pixel isless than zero, the respective pixel is made to appear transparent.

In another implementation, techniques are described to provide clearrectangles in a composite output of one or more video streams. Clearrectangles (e.g., transparent areas) to appear in the composite outputare configured. A texture is arrived at which represents a union of eachof the clear rectangles. The texture is applied on a pixel-by-pixelbasis to form the clear rectangles in the composite output. The texturearrived at may be applied to successive frames of the composite outputuntil a change is made to the clear rectangles. When a change occurs, anew texture is formed and applied.

In another implementation, capture techniques are described to providevideo capture of a main video stream in a composite output of one ormore video streams. An application may allocate a capture buffer insystem memory responsive to receiving a capture request. An image of themain video stream may be captured from a back buffer used to compositethe one or more video streams. This capture may occur after processingof the main video stream and before compositing of sub-streams on themain video stream. Access to the back buffer may be restricted to agraphics processor, thus a texture available to the graphics processorand the module is employed to copy the image to the capture buffer. Tocapture the image, the image of the main video stream is resolved intomultiple strips. Each strip is copied to the texture and then from thetexture to the capture buffer system memory. The strips arereconstructed in the capture buffer to form the captured image.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Theuse of the same reference numbers in different instances in thedescription and the figures may indicate similar or identical items.

FIG. 1 is an illustration of an environment in an exemplaryimplementation that is operable to employ high definition media contentprocessing techniques.

FIG. 2 is an illustration depicting an example of a client devicedescribed in FIG. 1 in greater detail.

FIG. 3 is a flow diagram depicting a procedure in an exemplaryimplementation of luma keying for composite output of one or more videostreams.

FIG. 4 is a flow diagram depicting a procedure in an exemplaryimplementation of clear rectangles for composite output of one or morevideo streams.

FIG. 5A is an illustration depicting an example representation of clearrectangles.

FIG. 5B is an illustration depicting an example representation of atexture to implement clear rectangles.

FIG. 6 is a flow diagram depicting a procedure in an exemplaryimplementation in which a texture is applied to form clear rectangles ina composite output of one or more video streams.

FIG. 7 is a flow diagram depicting a procedure in an exemplaryimplementation in which an image is captured by resolving strips of theimage into a texture to copy the image to a capture buffer of systemmemory.

DETAILED DESCRIPTION

Overview

Options that are available to users for media content are everincreasing. For example, more and more media content is available inhigh definition resolutions. Devices such as televisions and opticaldisk playback devices supporting high definition media content areincreasingly in demand. However, traditional techniques to render mediacontent on such devices may not be suitable for high definition mediacontent due to increased processing demands to handle the higherresolution.

High definition media content processing techniques are described inwhich one or more modules may perform enhanced rendering techniques tooutput high definition media content, as well as other media content. Inan implementation, luma keying (in which transparent region of compositeoutput may be specified) is provided using an optimum set of graphicsprocessing instructions. For instance, a client device may include arendering application which provides instructions to implement lumakeying on a graphics processing unit. The rendering application mayinstruct the graphics processing unit to determine a maximum value asthe greater of a pixel's luma value minus a high threshold and a lowthreshold minus the pixel's luma value. When the maximum value for arespective pixel is less than zero, the graphics processing unit (underthe influence of the rendering application) may set the respective pixelto appear transparent in the composite output.

In another implementation, techniques are described to provide clearrectangles (e.g., transparent rectangular regions) in a composite outputof one or more video streams. Clear rectangles permit regions of onecontent stream to appear through another, such as to expose a main videostream through a menu or subtitle stream. Clear rectangles which are toappear in the composite output are configured, for example by a mediaplayback application of a client device. Attributes defining the clearrectangles may be passed by the media playback application in a contentstream to a rendering application. The rendering application may usethese attributes to form a texture representing a union of each of theclear rectangles. A graphics processing unit (GPU) under the influenceof the rendering application may apply the texture on a pixel-by-pixelbasis to the video streams to form the clear rectangles in the compositeoutput. The texture may be set up initially and then may be applied tosuccessive frames of the composite output until a change is made to theclear rectangles. When a change occurs, a new texture may be formed andapplied. Thus, additional processing involved in forming the texturesover and over may be avoided.

In another implementation, capture techniques are described to providevideo capture of a main video stream in a composite output of one ormore video streams. An console application of a game console mayallocate a capture buffer in system memory responsive to receiving acapture request. For example, a viewer of a movie played back via thegame console may initiate a request to capture an image from the movie.A capture module may provide an interface to capture an image of themain video stream of the movie from a back buffer used to composite oneor more video streams for an output of the movie. To provide an image ofa main video stream without sub streams, menus, overlays and so forth,the capture may occur after processing of the main video stream andbefore compositing of sub-streams on the main video stream.

Access to the back buffer may be limited to a graphics processing unit(GPU) of the game console. Thus, an intermediate texture (allocated inmemory available to the GPU and the console application and executeableby a processor of the game console) may be used to copy the image to thecapture buffer. To reduce the size of the texture, the image of the mainvideo stream may be resolved into a multiple strips which are smallerthan the overall image. Each strip may be copied to the texture by theGPU and then by the console application or capture module from thetexture to the capture buffer system memory. This permits a relativelysmall texture to be used to perform the capture.

In the following discussion, an exemplary environment is first describedthat is operable to perform high definition media content processingtechniques. Exemplary procedures are then described that may be employedin the exemplary environment, as well as in other environments. Althoughthese techniques are described as employed within a media processingenvironment in the following discussion, it should be readily apparentthat these techniques may be incorporated within a variety ofenvironments without departing from the spirit and scope thereof.

Exemplary Environment

FIG. 1 is an illustration of an environment 100 in an exemplaryimplementation that is operable to employ high definition media contentprocessing techniques described herein. The illustrated environment 100includes a client device 102 and a display device 104. Client device 102is illustrated as connected to one or more content sources 106 via anetwork 108. Network 108 may be representative of one or more networksthrough which content sources 106 may be available including but notlimited to an intranet, the Internet, a broadcast network, a wirelessnetwork, a satellite network, and so forth.

Client device 102 may be configured in a variety of ways. For example,client device 102 may be configured as a computer that is capable ofcommunicating over the network 108, such as a desktop computer, a mobilestation, an entertainment appliance, a set-top box communicativelycoupled to a display device as illustrated, a wireless phone, and soforth. Client device 102 may also be configured a game console, furtherdiscussion of which may be found in reference to FIG. 2.

Client device 102 may interact via the network 108 to select and receivemedia content 110 available from the content sources 106. For example,client device 102 is depicted as having media content 112 which mayinclude media content 112 received via the network 108. Media content110 provided by the content sources 106 via the network 108 may beaccessed by the client device 102 for streaming playback, storage on theclient device 102, and so forth.

Media content 112 may also be obtained locally by the client device 102,such a being stored in memory 118 and/or provided from variouscomputer-readable media sources. A variety of computer-readable media iscontemplated including floppy disk, optical disks such as compact discs(CDs) and digital video disks (DVDs), a hard disk, and so forth. Forexample, client device 102 is illustrated a including a media drive 114through which media content 112 may be accessed for execution, playbackfrom the media drive and/or storage in memory 118.

In an implementation, media drive 114 may be configured as an opticaldisk drive to read optical disks holding data according to variousstandards and formats. Examples of optical disk formats suitable for amedia drive 114 include but are not limited to CD-ROM, DVD, and highdefinition optical disk formats such as HD-DVD (e.g., HD-DVD developedby the DVD Forum) and BLU-RAY (e.g., Blu-ray Disc format developed bythe Blu-ray Disc Association (BDA)). Other types and formats for mediadrive 114 and corresponding computer-readable media are alsocontemplated. While media drive 114 may be an internal drive asillustrated, media drive 114 may alternatively be configured as anexternal drive communicatively coupled to the client via a mediainterface. Further, a client device 102 may include multiple mediadrives 114 each configured to read data in different associated formats.

Media content 112 is representative of a variety of different types ofcontent, including but not limited to: video programs, televisionprograms, music, applications, games, internet pages, streaming videoand audio, and so forth. In an implementation, at least some of themedia content 112 of client device 102 is high definition content, suchas high definition video programs, movies, television programs, gamesand so forth. Examples of high definition content formats includecontent having resolutions of 720p, 1080i and 1080p content. Mediacontent 112 in high definition formats may be available via the mediadrive 114 reading optical disks, from storage in memory 118 and/or fromcontent sources 106 over the network 108.

While certain examples and techniques may be described herein withrespect to media content 112 in a high definition format, it iscontemplated that the techniques may be employed to enhance processingof other content formats, including media content 112 which is notconsidered high definition. Accordingly, the described techniques may beemployed to process media content 112 configured in various formats,alone or in combinations thereof. For example, different content streamshaving different formats can be composited into an output, such as in apicture-in-picture (PIP) or picture-by-picture (PBP) presentation.

Client device 102 also includes a processor 116, memory 118 andapplications 120 which may be stored in the memory 118 and executed viathe processor 116. Processors are not limited by the materials fromwhich they are formed or the processing mechanisms employed therein. Forexample, processors may be comprised of semiconductor(s) and/ortransistors (e.g., electronic integrated circuits (ICs)). In such acontext, processor-executable instructions may beelectronically-executable instructions. Additionally, although a singlememory 118 is shown for the client device 102, a wide variety of typesand combinations of memory may be employed, such as random access memory(RAM), hard disk memory, video memory, texture memory, removable mediummemory, and other types of computer-readable media.

Client device 102 may include various applications 120 to providefunctionality of the client device 102. Applications 120 provide with aclient device 102 may include but are not limited to: operating systemsoftware, utility software, a browser application, an electronicprogramming guide (EPG) application, office productivity programs, gameprograms, media management software, a media playback application, andso forth. A variety of other applications 120 are also contemplated.

In the depicted example, client device 102 also includes a communicationmodule 122 and a rendering module 124. Communication module 122represents functionality to interact with content sources 106 via thenetwork 108. In particular, the communication module 122 may representfunctionality to search, obtain, process, manage and initiate output ofmedia content 110 and/or other data that may be available from thecontent sources 106.

Rendering module 124 is representative of a variety of functionality toprocess media content 112 at the client device 102, such as display ofmedia content 112 on the display device 104. In particular, renderingmodule 124 may be executed to composite multiple video streams into acomposite output and to render the composite output in synch with apresentation clock. Rendering module 124 may be implemented as acomponent of operating system software. In another example, renderingmodule 124 may be implemented as a component of an application 120configured as a media playback application to manage and controlplayback of media content 112 on the client device 102. Rendering module124 may also be a stand-alone application that operates in conjunctionwith the operating system and/or a media playback application to outputmedia content 112 for display on the display device 104. A variety ofapplications 120 of a client device 102 may interact with and utilizethe features of the rendering module 124 to output media content 112.

In an implementation, rendering module 124 may be operable to outputcontent 112 that is configured in accordance with one or more HD-DVDspecifications (e.g., HD-DVD Specification version 1.0 promulgated bythe DVD Forum). The one or more HD-DVD specifications specify theinclusion of techniques for luma keying, clear rectangle, and imagecapture related to playback of HD-DVD content without specifying detailsas to how the techniques are to be implemented. Accordingly, in thiscontext rendering module 124 may be further configured to implementtechniques for luma keying, clear rectangles, and image capture furtherdiscussion of which may be found in reference to FIG. 2 and thefollowing figures. While the described techniques may be applicable toimplement aspects of one or more HD-DVD specifications, it iscontemplated that the described techniques for luma keying, clearrectangles and image capture are not limited to implementing HD-DVDspecifications, but rather are applicable to rendering media content 112of a variety of types and formats.

Client device 102 also includes a graphics processing unit (GPU) 126that is representative of various processing functionality of the clientdevice 102 which may be dedicated to graphics processing. Functionalityprovided by the GPU 126 may include controlling aspects of resolution,pixel shading operations, color depth, texture mapping, and other tasksassociated with rendering images such as bitmap transfers and painting,window resizing and repositioning, line drawing, font scaling polygondrawing, and so on. The GPU 126 may be capable of handling theseprocessing tasks in hardware at greater speeds than the softwareexecuted on the processor 116. Thus, the dedicated processing capabilityof the GPU 126 may reduce the workload of the processor 116 and free upsystem resources for other tasks. In an implementation, GPU 126 may beoperated under the influence of the rendering module 124 to perform thevarious processing functions. For instance, rendering module 124 may beconfigured to provide instructions to direct the operation of the GPU126, including processing tasks involved in techniques for luma keying,clear rectangles and image capture.

Results of the processing by rendering module 124 and/or GPU 126 may beoutput for display on the display device 104. Client device 102 includesa display interface 128 through which rendered media content may bedisplayed on a display device 104. Display interface 128 may incorporatea digital to analog converter (DAC), digital video interface (DVI)outputs and/or other components to convert the rendered media content112 into a form understandable by the display device 104.

Generally, the functions described herein can be implemented usingsoftware, firmware, hardware (e.g., fixed-logic circuitry), manualprocessing, or a combination of these implementations. The terms“module”, “functionality”, “engine” and “logic” as used herein generallyrepresent software, firmware, hardware, or a combination thereof. In thecase of a software implementation, for instance, the module,functionality, or logic represents program code that performs specifiedtasks when executed on a processor (e.g., CPU or CPUs). The program codecan be stored in one or more computer-readable memory devices. Thefeatures of the techniques to provide high definition media contentprocessing are platform independent, meaning that the techniques may beimplemented on a variety of commercial computing platforms having avariety of processors.

FIG. 2 is an illustration of an embodiment of an exemplary device 200illustrating aspects of the client device 102 of FIG. 1 in greaterdetail. In the depicted example, the client device 102 of FIG. 1 isillustrated as a game console 202. Game console 202 may provide avariety of gaming interactions, such as playback of game discs, andnetwork gaming sessions, as well as other interactions with mediacontent 112. The game console 202 is illustrated as having a media drive114, processor 116, memory 118, graphics processing unit 126 and displayinterface 128 coupled to a display device 104, as discussed in relationto FIG. 1.

The processor 116 is illustrated as executing a console application 204.The console application 204 provides a consistent user interface andnavigation features to move users through various entertainment areas.The console application 204 offers a convenient way to access contentfrom multiple different types of media content 112 (e.g., game data,audio data, Internet data; video data and so forth) regardless of themedia type which is accessed from the media drive 114, memory 118, orfrom a other content sources 106 of FIG. 1. When the game console 202 ispowered on, the console application 204 may be executed on the processor116. The console application 204 presents a graphical user interfacethat provides a consistent user experience when navigating to interactwith different media content 112 on the game console 202. The consoleapplication 204 thus provides integrated functionality to access,manage, store and interact with media content 112 of the game console202. As illustrated, the console application 204 may include thecommunication module 122 and rendering module 124 of FIG. 1 ascomponents thereof.

As noted, rendering module 124 may include functionality to performtechniques related to luma keying, clear rectangle, and image capture.In the example depicted in FIG. 2, rendering module 124 includes a lumakeying module 206 representative of functionality executable toimplement luma keying techniques, further discussion of which may befound in reference to FIG. 3. Rendering module 124 is also illustratedas including a clear rectangle module 208 representative offunctionality executable to implement clear rectangle techniques,further discussion of which may be found in reference to FIGS. 4-6.Rendering module 124 also is illustrated as including a capture module208 representative of functionality executable to implement imagecapture techniques, further discussion of which may be found inreference to FIG. 7.

As noted, memory 118 may be representative of various types of memorythat may be included with a game console 202, such as random accessmemory (RAM), read only memory (ROM), system memory, video memory(VRAM), hard disk storage and so forth. Memory 118 of the example gameconsole 202 of FIG. 2 includes hard disk storage 212, which may store avariety of different data, examples of which include but are not limitedto: applications 120, media content 112, and various application/gamedata 214, as illustrated in FIG. 2.

Memory 118 may also includes various memory surfaces 216 which may bearranged to perform rendering of media content 112. For instance, therendering module 124 may arrange and manage various memory surfaces 216to be used in performance of graphics processing operations. Examples ofmemory surfaces 216 include input 218 and output 220 memory surfaces,which may be arranged to hold/sequence input data for processing tasksperformed on media content 112 tasks and to store the results ofprocessing tasks for additional processing and/or output. The input 218and output 220 memory surfaces may also be representative of variousbuffers used in the processing of media content 112, including thecapture buffer and back buffer discussed in relation to FIG. 7.

Memory surfaces 216 of FIG. 2 are also illustrated as having a texture222. The illustrated texture 222 is representative of one or moretextures which may be stored within memory 118 or other suitable memory.The texture 222 may be configured as a bit map indicative of variouscharacteristics such as color, transparency, shading and so forth.Texture 222 may configured to be employed to represent a union of clearrectangles as discussed in relation to FIG. 4-6. Another texture 222 maybe used to implement image capture techniques discussed in relation toFIG. 7. Texture 222 may be formed in memory 118 and may be appliedrepeatedly during iterative processing tasks.

Further, memory surfaces 216 may include a desktop 224 surface to whichprocessed data ready for display on the display device 104 may bewritten. For example rendering module 124 may manage sequencing ofwriting frame data to the desktop 224 surface, which may then berendered via display interface 128 for presentation on the displaydevice 104.

GPU 126 may also include memory 226 which is dedicated to processingtask of the GPU 126 and may be accessible to the GPU 126 alone forsecurity purposes. It is noted that while the various memory surfaces216 are depicted in FIG. 2 as arranged in memory 118 (e.g., systemmemory), the memory surfaces 216 may be arranged in various combinationsamong memory 118, memory 226 of the GPU 126 and/or other suitablememory. Thus, high definition media content processing techniquesdescribed herein portions may involve portions of memory 118 dedicatedto the game console 202 (e.g., dedicated system memory), portions ofmemory 118 shared by the system and GPU 126 (e.g., shared VRAM), andportions of memory 226 of the GPU 126 dedicated to the GPU 126.

Further, cryptographic techniques may be employed to operate on andsecure protected content. For instance, game console 202 may alsoinclude a cryptographic module 228, which in the example of FIG. 2 isillustrated as a component of the GPU 126. Cryptographic module 228 mayalso be implemented in hardware and/or software as a standalonecomponent of the game console 202. Cryptographic module 228 isrepresentative of functionality to perform various secure encoding anddecoding operations to secure various memory portions and implementsecurity measures when rendering media content 112, such as to preventpiracy of protected media content.

GPU 126 is also illustrated as having a pixel shader 230. The pixelshader 230 is representative of functionality to perform variouspixel-by-pixel operations on media content 112 rendered via the GPU 126.In an implementation, pixel shader 230 is operated under the influenceof the rendering module 124, through processing instructions from therendering module 124 to control the GPU 126. Pixel shader 230 may beoperated to implement aspects of techniques for luma keying and clearrectangles, further discussion of which may be found in relation to FIG.3 and FIGS. 4-6 respectively.

An input device 232 is also illustrated which is representative of adevice that may be manipulated by a user to form inputs to operate thegame console 202. For instance, input device 232 may be manipulated toprovide various inputs to navigate the console application 204, selectmedia content 112, play games, and so forth. Input device 232 may beconfigured as game controller as illustrated in FIG. 2. A variety ofother input devices are also contemplated for use with the game console202 and/or the client device 102 of FIG. 1, such as a mouse, keyboard,trackball and so forth.

Exemplary Procedures

The following discussion describes techniques related to high definitionmedia content processing that may be implemented utilizing thepreviously described environment, systems and devices. Aspects of eachof the procedures may be implemented in hardware, firmware, or software,or a combination thereof. The procedures are shown as a set of blocksthat specify operations performed by one or more devices and are notnecessarily limited to the orders shown for performing the operations bythe respective blocks. In portions of the following discussion,reference may be made to the exemplary environment 100 of FIG. 1 and thedevice 200 of FIG. 2.

Luma Keying

Luma keying allows content authors specify transparent regions within acomposite output of multiple content sub-streams while using a compactvideo format. The multiple content streams may include for example mainvideo, sub video, menu overlays, graphics overlays, text overlays, andso forth, which are layered one over another to produce the compositeoutput. In particular, the luma keying techniques may be implementedwithout using a separate alpha channel in the content stream data tocontain transparency data.

Rather, upper and lower limits for luma (e.g., brightness) areestablished for a content stream. In processing the content stream,calculations are performed to check the luma value of each pixel to beoutput against the upper and lower limits. When it is determined thatthe luma for a particular pixel falls within the upper and lower limits,then that pixel is made transparent.

Referring to FIG. 3, a procedure 300 is depicted in an exemplaryimplementation in which luma keying is performed for media contentrendering by a client device. An upper limit and a lower limit for lumaof a content stream are received (block 302). For example, playback ofmedia content 112 from an optical disk inserted in the media drive 114of game console 202 may be initiated through interactions with theconsole application 204. For the purposes of example, assume the opticaldisk contains a movie in HD-DVD format. Rendering module 124 may beexecuted to render the movie for output on the display device 104.Rendering module 124 processes data for the movie from the optical diskwhich may include multiple content streams to be composited to form thecomposite output. Luma keying module 206 may be executed to cause lumakeying to be performed on the composited streams.

Luma keying may be configured by including and setting attributesrelated to luma keying for each content stream. The attributes maycontain a structure that specifies whether or not luma keying is enabledfor the stream and an upper and lower luma limit for the content stream.The upper limit and lower limit for luma may be extracted by the lumakeying module 206 from the content and passed to the GPU 126 along withinstructions to initialize processing of pixels of the content stream.If the attributes indicate that luma keying is disabled, then lumakeying processing for the content stream may be bypassed. It is notedthat the attributes, including the upper limit and lower limit for luma,may be set by a content author to change for each frame of a contentstream and/or set to remain the same for a sequence of frames. Thisprovides content authors a great amount of flexibility in setting theattributes to use luma keying techniques described herein. GPU 126receives the limits and processing instructions and performs theprocessing specified by the instructions.

For each pixel of the content stream, a maximum value is determined asthe greater of a luma value of the pixel minus the upper limit and thelower limit minus the luma value of the pixel (block 304). When themaximum value determined for a respective pixel is less than zero, therespective pixel is set to appear transparent (block 306).

For example, the instructions from the luma keying module 206 may beperformed as part of operations of the pixel shader 230 component of theGPU 126. The pixel shader 230 under the influence of rendering module124 and/or luma keying module 206 performs a variety of processing on apixel-by-pixel basis. In particular, the pixel shader 230 may operate oneach pixel in each frame of the content stream. For high definitioncontent, such as content having a resolution of 1920×1080 pixels, thismay equate to processing of two million plus pixels per frame. Further,because multiple content streams may be composited to form a compositeoutput, the number of pixels processed for a frame of the compositeoutput may equate to two million plus pixels times the number of contentstreams.

Accordingly, performance gains may be achieved by optimizing the numberof processing instructions performed and/or avoiding branches in theexecution of the processing instructions. Thus, the luma keyingtechniques herein may be implemented using relatively few processinginstructions within the rendering module 124 or luma keying module 206to cause operations by the pixel shader 230. Further, the processinginstructions to implement luma keying may be configured to avoid usingbranch instructions since using branch instructions may introduceoverhead of several instructions per pixel processed.

In an implementation, performance is achieved by implementing lumakeying using relatively few processing instructions. Accordingly, theseprocessing instructions may be executed relatively quickly by the GPU126 and/or pixel shader 230. In one or more embodiments, about four orfewer processing instructions are used to cause the pixel shader 230 foreach pixel to:

-   -   Subtract the upper limit from the pixel's luma value.    -   Subtract the pixel's luma value from the lower threshold.    -   Determine a maximum value from the above calculations.    -   When the maximum is less than zero, then the luma keying is        active and the pixel is made transparent.        If the maximum is not less than zero, then the pixel's        transparency is not changed, e.g., the pixel is not operated        upon to change the transparency.

In an implementation, processing instructions used for the describedluma keying techniques may be configured as assembly languageinstructions that are performable by the pixel shader 230. An example ofsuch assembly language instructions is provided as follows:

// Luma Key the Y channel // constant c11 is the upper bound // constantc10 is the lower bound // r0 contains the input pixel data // r1 is usedto return the output pixel data // r3, r4, and r5 are temporaryvariables sub r3.x, r0.x, c11.x // r3.x = r0.x − upper.x sub r4.x,c10.x, r0.x // r4.x = lower.x − r0.x max r5.x, r3.x, r4.x // r5.x =max(r3.x, r4.x) cmp r1.a, r5.x, r0.a, c0.a // r1.a = (r5.x >= 0) ? r0.a:0The preceding example is but one example of processing instructions thatmay be used to implement the described luma keying techniques. A varietyof other examples of processing instructions to implement luma keyingtechniques are also contemplated.

The content stream having the resultant pixels is output (block 308).For example, the rendering module 124 may output the HD-DVD movie on thedisplay device 104 of FIG. 2 having clear pixels that are the result ofluma keying processing by the GPU 126 and/or pixel shader 230. In thismanner, luma keying may be implemented to include transparent regionswithin a composite output of multiple content sub-streams.

Clear Rectangle

Clear rectangle allows content authors to specify rectangular regions incontent streams of a composite output to be made transparent so that anunderlying content stream is visible in the composite output. Multipleclear rectangles may be specified. In an implementation, up to 32simultaneous clear rectangles may be supported. Further, each clearrectangle may span multiple content streams, may overlap with otherclear rectangles, and can have different target z-depths.

Z-depth as used herein refers to the relative position of contentstreams one to another in a composite output. A main content or videostream may have a z-depth of zero. In creating the composite output, astream of zero z-depth may be composited first, e.g., on the “bottom”.Additional content streams may be layered on top of the “bottom” streamon the basis of respective z-depths. For instance, the rendering module124 may be configured to composite streams in order from lowest tohighest z-depth. Thus, z-depth one is rendered above z-depth zero,z-depth two is rendered above z-depth one, and so on.

In relation to clear rectangles, target z-depth indicates which layersor streams the clear rectangle penetrates. For example, a clearrectangle may be defined to begin at a z-depth of two and extend to az-depth of one. Thus, an underlying stream of z-depth one will beexposed by the example clear rectangle. However, a stream of z-depththree will cover the clear rectangle and the underlying stream, sincethe example clear rectangle does not extend through z-depth three.

FIG. 4 depicts a procedure 400 in an exemplary implementation in whichclear rectangles are constructed. In discussing FIG. 4, reference willbe made to example representation of clear rectangles depicted in FIG.5A and the example representation of a texture used to implement clearrectangles depicted in FIG. 5B.

Processing to combine video streams into a composite output is initiated(block 402). For example the rendering module 124 of FIG. 1 may beexecuted to playback media content 112 on the client device 102, such ason the display device 104. In an embodiment, the rendering module 124may include clear rectangle module 208, as in FIG. 2, to implementaspects of the described clear rectangle techniques. For the purposes ofexample, the media content 112 may be a high definition televisionprogram which is downloaded from a content source 106 and recorded tomemory 118 of the client device 102. In another example, the mediacontent 112 may be configured as a movie stored on an optical disk andplayed back from the media drive 114. Rendering module 124 may operateto composite multiple video streams from the media content 112 into acomposite output. The composited video stream may also include menu,text, graphics and other overlays from the media content 112 and/or fromother sources, such as a menu or guide streams from the rendering module124 or from an associated application 120 configured for media playback.To perform the compositing of multiple streams, the rendering module 124may be configured to initiate various rendering operations and mayprovide instructions to direct GPU 126 to perform certain operations.Thus, rendering module 124 may be executed to initiate processingrelated to playback of the television program from memory 118 or toinitiate playback of the movie from the media drive 114.

Data defining clear rectangles that are to appear in the compositeoutput is obtained (block 404). For example, in playback of thetelevision program in the preceding example, one or more clearrectangles may be defined, for instance to show main video of thetelevision program through other streams such as a subtitle streamand/or a program guide stream.

In an implementation, attributes defining clear rectangles may beobtained via one or more of the composited content streams. Clearrectangles may be defined by a content author and may be configured byan application 120 which may include media playback functionality, forexample the console application 204. The configured clear rectangles maybe passed to the rendering module 124 and/or clear rectangle module 208via the attributes to implement the clear rectangles.

In particular, attributes defining clear rectangles may be attached oneor more content streams. In an implementation, the attributes definingclear rectangles for a composite output are associated with the zeroz-depth stream, e.g., the main video stream. The attributes may indicatea number of clear rectangles to be included, the maximum z-depth of theset of rectangles, and an array of structures to define each individualclear rectangle. The array of structures may include a structure foreach rectangle having the target z-depth and coordinates of therespective rectangle. The attributes defining clear rectangles, andaccordingly the defined rectangles, may be changed for each frame of acontent stream. Of course, the attributes defining clear rectangles mayalso remain the same for multiple consecutive frames to maintain adefined arrangement of clear rectangles through the consecutive frames.

Referring to FIG. 5A, a diagram 500 depicts an example representation ofclear rectangles in a composite output. For example, FIG. 5A shows fourvideo streams which may be composited to form a composite output. Anapplication 120 configured for media playback may direct the renderingmodule 124 to perform the compositing. The video streams in this exampleinclude main video 502(0), sub video 502(1), subtitle 502(2), andgraphics 502(3). The numbers within the parentheses in the referencesnumbers for the streams correspond to the respective z-depths of thestream. It is noted that the streams are composited in order ofincreasing z-depth.

The application 120 may configure four clear rectangles which are shownas clear rectangles 504(1)-504(4) in FIG. 5A. The application 120specifies that clear rectangles 504(1) and 504(3) span video streamswith z-depth of one and two. The application 120 specifies that theclear rectangles 504(2) and 504(4) span only the stream with z-depth oftwo. In addition, it may be seen that the clear rectangles 504(3) and504(4) are overlapping.

In this example, the application may attach or otherwise associateattributes to the main video 502(0) stream which defines the clearrectangles. For instance, the associated attributes may indicate thatthere are four rectangles, the coordinates of each of the fourrectangles, and a maximum z-depth of each of the clear rectangles, whichis two in the example of FIG. 5A. In addition, attributes may indicatethat clear rectangles 504(1) and 504(3) have a target z-depth of one andalso indicate that clear rectangles 504(2) and 504(4) have a targetz-depth of two. The application 120 may communicate the attributesdefining the clear rectangles 504(1)-504(4) to the rendering module 124and/or clear rectangle module 208. Rendering module 124 and/or clearrectangle module 208 may then use the obtained attributes to implementthe clear rectangles 504(1)-504(4).

Referring again to FIG. 4, a texture to represent a union of the clearrectangles is formed (block 406). For instance, to implement clearrectangles 504(1)-504(4) of FIG. 5A, rendering module 124 and/or clearrectangle module 208 of FIG. 2 may form a texture 222. The texture 222illustrated in FIG. 2 may be representative of various texturesincluding textures used to implement clear rectangles. The texture 222may be within memory 118 of the game console 202 as depicted in FIG. 2or in other suitable memory, such as memory 226 of the GPU 126. Thetexture 222 may be configured as a bitmap representative of the union ofthe clear rectangles 504(1)-504(4).

More particularly, when clear rectangle is enabled for the first time,or when the number or dimensions of clear rectangles for a compositeoutput change, a rectangular texture may be formed and stored in memory,such as the texture 222 in FIG. 2. The texture that is formed may use aone byte per pixel linear format that represents the union of each ofthe clear rectangles. The first time clear rectangle is enabled, thetexture may be initialized so that each byte has the sentinel value.When clear rectangles have previously been configured, the clearrectangles are removed from the texture by setting each byte of memoryin the texture corresponding to the clear rectangles to the sentinelvalue. In an implementation, the sentinel value may be set to 255. Thesentinel value may represent an upper bound on the z-depth. Forinstance, when the value is 255, the texture may support clearrectangles for up to 255 streams (e.g., z-depth from 0 to 254). Othersentinel values may also be employed with the clear rectangle techniqueswithout departing from the spirit and scope thereof.

In an implementation, each of the defined clear rectangles is processedin order from highest target z-depth to lowest target z-depth to set-upthe texture. This ensures that if two or more clear rectangles overlap,the transparency will extend to the lowest z-depth in the overlappingregion. To process each clear rectangle, each byte of memory in thetexture corresponding to the area within the clear rectangle is set tothe value of the clear rectangle's target z-depth. The sentinel value isretained in each byte of memory in the texture that does not correspondto clear rectangles. The result is a texture representing the union ofthe defined clear rectangles. In particular, the texture may be formedto include the lowest z-depth of clear rectangles in areas of thetexture which are to have clear rectangles and the sentinel value in theremaining areas of the texture. Once the clear rectangle texture is setup, it may be used during video processing to determine whether to makepixels for each stream transparent.

Referring to FIG. 5B, a diagram 506 depicts an example representation ofa texture 508 to implement the clear rectangles of FIG. 5A. It may beseen that the sentinel value, in this example 255, is included inregions 510 of the texture 508 which do not correspond to clearrectangles 504(1)-504(4) of FIG. 5A. Regions of texture 508 thatcorrespond to the clear rectangles 504(1)-504(4) are labeledaccordingly. These regions contain the target z-depth of respectiverectangles. For example, the region of the texture 508 corresponding toclear rectangle 504(1) has the value of one. In the area of overlapping,the lowest target z-depth is contained in the texture 508. For example,the region of the texture 508 corresponding to the overlap of clearrectangles 504(3) and 504(4) has the value of one, which is the lowertarget z-depth of clear rectangle 504(3).

Referring again to FIG. 4, the texture is applied on a pixel-by-pixelbasis to the video streams to form the clear rectangles in the compositeoutput (block 408). For instance, the texture 508 of FIG. 5B may beapplied to implement clear rectangles 504(1)-504(4) of FIG. 5A. Forexample, the rendering module 124 and/or clear rectangle module 208 mayprovide the texture 508 and processing instructions to cause the GPU 126to apply the texture. Additional discussion of processing techniques toapply a texture to implement clear rectangles may be found in relationto procedure 600 of FIG. 6.

The composite output having the resultant clear rectangles is providedfor display (block 410). For example, when the texture 508 has beenapplied by the GPU 126, the composite output formed may be returned tothe application 120 for display. For instance, the rendering module 124may cause a frame of composite output to which the texture 508 has beenapplied to be written into a desktop 224 memory surface which may beoutput via the display interface 128 on the display device 104. Theframe of composite output is configured to include the clear rectangles504(1)-504(4) of the preceding examples.

The rendering module 124 and/or GPU 126 may apply the texture 508successively to frames of the composite output until a change is made tothe clear rectangles. Accordingly, monitoring may be performed to detecta change in the clear rectangles (block 412). The changes in the clearrectangles may be determined through monitoring of the attributesdefining the clear rectangles. When a change is detected, the procedure400 may return to block 406 where a new texture may be formed torepresent the changed rectangles. When no change is detected, theprocedure 400 may return to block 408 where rendering module 124 and/orGPU 126 may continue to apply the previously formed texture.

FIG. 6 depicts a procedure 600 in an exemplary implementation in which atexture is applied to form clear rectangles in a composite output of oneor more video streams. A texture and stream Z-depth associated with avideo stream is received to apply the texture to the video streampixel-by-pixel (block 602). For instance, rendering module 124 of FIG. 2may operate to pass a texture which is formed in accordance withprocedure 400 of FIG. 4, such as texture 508, to GPU 126 to apply thetexture to a video stream for a composite output. Rendering module 124may also pass the z-depth of the stream and processing instructions tothe GPU 126. The GPU 126 and/or particular pixel shader 230 of the GPUmay execute the instructions to apply the texture to the video stream.

A determination is made as to whether clear rectangle processing isenabled for the video stream (block 604). In an implementation, thedetermination may involve determining if the z-depth associated with avideo stream is greater than zero. When clear rectangle is not enabled,clear rectangle processing is bypassed for the video stream (block 606).

For instance, during video processing, the video frames for each contentstream are composited on top of the main video stream in order ofincreasing z-depth. In order to determine whether clear rectangle isenabled for a particular video stream, the maximum clear rectanglez-depth is compared to the video stream's z-depth. The rendering module124 may be executed to make this comparison. If the stream's z-depth isless than or equal to the maximum clear rectangle z-depth, then clearrectangle is enabled for that stream, and the GPU and/or pixel shader230 may be instructed to handle the transparency test for each pixel.When clear rectangle is enabled for the video stream, then both thepreviously configured texture and the z-depth of the video stream may bepassed in to the pixel shader 230 for processing. Otherwise, a value ofzero is associated with the stream and passed in as the stream'sz-depth. This tells the GPU and/or pixel shader 230 to bypass the clearrectangle processing.

When clear rectangle is enabled, the GPU and/or pixel shader 230 areexecuted to perform operations to apply the texture. The pixel shader230 may execute once for each pixel. The pixel shader 230 determineswhether the pixel is within a clear rectangle and if so makes the pixeltransparent.

In particular, for each pixel, the texture is referenced to determine acorresponding lookup value (block 608). For example, the texture lookupmay use the normalized screen coordinates of the pixel that is currentlybeing processed to obtain a corresponding value from the texture. Forexample, a lookup may be performed on a texture 222 stored on gameconsole 202 of FIG. 2. The texture 222 may be configured in accordancewith the techniques discussed with respect to FIG. 4 and the exampletexture 508 of FIG. 5B. The lookup will determine the lowest z-depth ofeach clear rectangle that overlaps the pixel. In areas where there areno clear rectangles, the lookup will return the sentinel value.

A determination is made whether the value from the lookup is less thanor equal to the stream's z-depth (block 610). The determination assesseswhether the pixel being processed is within a clear rectangle andaccordingly is to be made transparent. If the result of the texturelookup is greater than the streams z-depth, then the pixel is outsidethe clear rectangle and the transparency of the pixel is not changed(block 612). If the result of the texture lookup is less than or equalto the stream's z-depth, then the pixel is determined to be within aclear rectangle, and is made transparent (block 614). For instance,pixel shader 230 may set an alpha channel of the pixel to zero to makethe pixel transparent. It is noted that the sentinel value used forareas in the texture outside of clear rectangle regions may be selectedso that the value is greater than the number of possible streams. Inthis way, when the sentinel value is returned in the texture lookup itwill be greater than the highest possible stream z-depth.

Image Capture:

Image capture allows a snapshot to be taken, in bitmap form, of thecurrent video frame from the main video stream. In an implementation,the capture is done after video processing has been performed (such asscaling, color conversion, brightness/contrast adjustments), but beforesub-streams have been composited on top of the main video. In addition,letterboxing or pillar boxing is removed from the final captured image.In traditional techniques, captured image contained the fully compositedimage including sub-titles and graphics.

Image capture may be implemented via the rendering module 124 describedherein. In an embodiment, rendering module 124 includes a capture module210 as illustrated in FIG. 2 to implement image capture techniques. Thecapture module 210 may incorporate a capture interface off of a videomixer of the rendering module 124 used to composite content streams intoa composite output.

In operation, an application 120, such as the console application 204 oranother application 120 to provide interaction with media content 112may allocate a capture buffer. For example, capture buffer may bearranged in a portion of memory 118 accessible to the application 120and the processor 116 on which the application is executed. In otherwords the capture buffer may be in system memory. The application 120may then call into the interface of the capture module 210 to fill thebuffer with a snapshot of the main video stream post-video processingand before compositing sub-streams. When the interface is invoked, therendering module 124 may set a flag in the video mixer notifying it toperform an image capture. Rendering module may also pause or block theapplication's thread to permit the image capture to be completed.

To composite multiple content streams, the rendering module 124 may callinto a video processor (e.g., GPU 126) once for each content stream inorder from lowest to highest z-depth. The GPU 126 performs processingunder the influence of the rendering module 124 to composite the streamsonto a back buffer, which may be allocated in memory 226 of the GPU 126.In an implementation, access to the back buffer may be restricted to theGPU 126. Thus, the application 120 may not be able to directly copy theback buffer to the capture buffer. Instead the back buffer may beresolved to a texture which is accessible to both the GPU 126 and thesystem (e.g., application 120 and processor 116), such as the exampletexture 222 depicted in FIG. 2.

The image may be copied to the texture and then to the capture buffer.In an implementation, a texture of a certain size is allocated and theimage in the back buffer is resolved as a plurality of strips that fitinto the texture. The texture size used may be smaller than the size ofthe entire image. Thus, resolving the back buffer into strips may reducethe size of memory consumed by the texture and accordingly, the amountof memory which may be provided with a client device 102 or game console202 to support image capture.

FIG. 7 is a flow diagram depicting a procedure 700 in an exemplaryimplementation in which an image is captured by resolving strips of theimage into a texture to copy the image to a capture buffer of systemmemory.

A capture request is received from a requesting entity to capture aframe of the composite output (block 702). For example, a user watchinga movie played back using the media drive 114 of on the game console 202of FIG. 2, may manipulate the input device 232 to cause a capturerequest to be provided via the console application 204 or anotherapplication 120 configured to playback the movie. Console application204 may communicate the request to the capture module 210 to initiatethe image capture.

A capture buffer is allocated in system memory to store the frame whencaptured (block 704). In the preceding example, console application 204may allocate a capture buffer in system memory 118 responsive toreceiving the capture request from the user. In another example, thecapture module 210 may be configured to allocate a capture buffer whenthe request is processed.

Contents of a back buffer used to composite multiple streams to form thecomposite output are resolved into a plurality of strips (block 706).Each of the strips is copied to the capture buffer, the strips beingcopied one at a time into a texture and from the texture the capturebuffer (block 708). For example, when the capture request is received,then capture module 210 may operate to capture an image of the mainvideo stream from a back buffer used to composite the one or more videostreams into the composite output. The contents of the back buffer maybe captured after processing the main video stream. This allows thecaptured image to reflect each video processing step that was done onthe main video stream.

In order to reduce memory usage by the image capture operation, arelatively small texture is used as noted above. The image in the backbuffer is resolved in strips from top to bottom until the entire desiredimage is copied to the texture. Access to the back buffer may berestricted to GPU 126, thus the texture is established in memoryavailable to the GPU 126 and an application 120 employed to copy theimage to the capture buffer. Each strip is copied to the texture andthen from the texture to the capture buffer system memory.

In an implementation, the GPU 126 under the influence of the capturemodule 210 may be executed to successively copy strips of back buffer tothe texture. Capture module 210 may operate to copy strips from thetexture to the capture buffer. Thus, GPU 126 may fill the texture withone of the strips. Capture module 210 copies the one strip from thetexture to the capture buffer. The GPU 126 fills the texture withanother strip. Capture module 210 copies this other strip to the capturebuffer and so on, until the entire image is copied to the capturebuffer.

The texture may be as wide as the back buffer and an interval of theheight. For example, to capture a high definition image having aresolution of 1920 pixels by 1080 pixels, a texture may be set to thewidth of the back buffer, which in this example would be 1920 pixels.The height of the texture may be selected to balance processing speed,performance and memory usage and to optimize the image capture. Forinstance, a texture may be used which is 64 pixels high. At 4 bytes perpixel, this results in a texture that is 480 KB compared to about 8 MBif a single texture (1920 pixels by 1080 pixels) was used to resolve theentire back buffer at once. It is contemplated that various texturesizes may be used with the described image capture techniques withoutdeparting from the spirit and scope thereof.

The captured frame is reconstructed in the capture buffer from thestrips (block 710). For example, when each strip of the back buffer iscopied to the capture buffer, the entire image is in the capture buffer.Once the entire image has been copied, the application's thread issignaled and may perform additional processing to format, reconstruct orotherwise process the captured image. For example, the consoleapplication 204 (or other application 120) may perform a colorconversion to convert the captured image data from a color space of theback buffer to a suitable color space for output. The color conversionmay be performed by the application 120 rather than the GPU 126 toprevent overburdening of the GPU 126. In an implementation, the backbuffer may be YCbCr color space, such as YCbCr_709, or YCbCr_601. Thus,image data maybe converted from YCbCr to an RGB color space or othercolor space suitable for the game console 202 and/or a display device104. Then, the captured image is output to the requesting entity (block712). For example, the captured image may be stored as an image file inmemory 118, output to the user via the console application 204 on thedisplay device 104, and so forth.

CONCLUSION

Although the invention has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the invention defined in the appended claims is not necessarilylimited to the specific features or acts described. Rather, the specificfeatures and acts are disclosed as exemplary forms of implementing theclaimed invention.

What is claimed is:
 1. One or more computer-readable storage devicecomprising instructions that are stored thereon and are executable on aclient to perform acts comprising: initiating processing on the clientof media content having one or more video streams to combine the one ormore video streams into a composite output; receiving data defining oneor more clear rectangles to include in the composite output; forming atexture to represent a union of the one or more clear rectangles; andapplying the texture on a pixel-by-pixel basis to the one or more videostreams to form the clear rectangles in the composite output.
 2. One ormore computer-readable storage device as recited in claim 1, wherein theapplying of the texture on a pixel-by-pixel basis to the one or morevideo streams comprises, for each said video stream: communicating thetexture and a z-depth value associated with a respective said videostream to a graphics processing unit of the client to apply the texture;determining when clear rectangle processing is enabled for therespective said video stream, wherein the clear rectangle processing isenabled when the z-depth value associated with the respective said videostream is greater than zero; when the clear rectangle processing is notenabled, bypassing the clear rectangle processing for the respectivesaid video stream; when the clear rectangle processing is enabled;instructing the graphics processing unit to process the respective saidvideo stream pixel-by-pixel including for each said pixel: determiningwhen a corresponding lookup value referenced from the texture is lessthan or equal to the z-depth value associated with the respective saidvideo stream; and when the lookup value is less than or equal to thez-depth value associated with the respective said video stream, settingthe pixel to appear transparent in the composite output.
 3. One or morecomputer-readable storage device as recited in claim 1, wherein thetexture is configured as a bit-map that includes: for each byte in thetexture that does not correspond to an area where the one or more clearrectangles are defined, a sentinel value; and for each byte in thetexture that corresponds to an area where the one or more clearrectangles are defined; a z-depth value corresponding to a lowestz-depth of the one or more clear rectangles that overlap the byte. 4.One or more computer-readable storage device as recited in claim 1,wherein the data defining the one or more clear rectangles iscommunicated as attributes in a main video stream for the compositeoutput.
 5. One or more computer-readable storage device as recited inclaim 1, wherein the client is configured as a game console.
 6. One ormore computer-readable storage device as recited in claim 1, wherein themedia content comprises high definition media content obtained from anoptical disk via a media drive associated with the client.
 7. One ormore computer-readable storage device as recited in claim 1 where theinstructions are further executable to perform acts comprising:monitoring to detect a change in the data defining the one or more clearrectangles; when the change is detected, updating the texture torepresent the union of one or more clear rectangles as changed; andapplying the updated texture to include the one or more clear rectanglesas changed in the composite output.
 8. A method implemented by a clientdevice to form clear rectangles in a composite video output comprising:initiating processing on the client device of media content having oneor more video streams to combine the one or more video streams into thecomposite video output; receiving data defining one or more clearrectangles to include in the composite video output; forming a textureto represent a union of the one or more clear rectangles; and applyingthe texture on a pixel-by-pixel basis to the one or more video streamsto form the clear rectangles in the composite video output.
 9. Themethod as recited in claim 8, wherein the applying of the texture on apixel-by-pixel basis to the one or more video streams comprises, foreach said video stream: communicating the texture and a z-depth valueassociated with a respective said video stream to a graphics processingunit of the client to apply the texture; determining when clearrectangle processing is enabled for the respective said video stream,wherein the clear rectangle processing is enabled when the z-depth valueassociated with the respective said video stream is greater than zero;when the clear rectangle processing is not enabled, bypassing the clearrectangle processing for the respective said video stream; when theclear rectangle processing is enabled; instructing the graphicsprocessing unit to process the respective said video streampixel-by-pixel including for each said pixel: determining when acorresponding lookup value referenced from the texture is less than orequal to the z-depth value associated with the respective said videostream; and when the lookup value is less than or equal to the z-depthvalue associated with the respective said video stream, setting thepixel to appear transparent in the composite video output.
 10. Themethod as recited in claim 8, wherein the texture is configured as abit-map that includes: for each byte in the texture that does notcorrespond to an area where the one or more clear rectangles aredefined, a sentinel value; and for each byte in the texture thatcorresponds to an area where the one or more clear rectangles aredefined; a z-depth value corresponding to a lowest z-depth of the one ormore clear rectangles that overlap the byte.
 11. The method as recitedin claim 8, wherein the data defining the one or more clear rectanglesis communicated as attributes in a main video stream for the compositeoutput.
 12. The method as recited in claim 8, wherein the client deviceis configured as a game console.
 13. The method as recited in claim 8,wherein the media content comprises high definition media contentobtained from an optical disk via a media drive associated with theclient device.
 14. The method as recited in claim 8 further comprising:monitoring to detect a change in the data defining the one or more clearrectangles; when the change is detected, updating the texture torepresent the union of one or more clear rectangles as changed; andapplying the updated texture to include the one or more clear rectanglesas changed in the composite output.
 15. A game console comprising: agraphics processing unit (GPU); and one or more modules executable todirect the GPU to perform operations to produce clear rectangles in acomposite video output, the operations including: combining one or morevideo streams of media content into the composite video output; forminga texture to represent a union of one or more clear rectangles definedfor inclusion in the composite video output; and causing the GPU toapply the texture on a pixel-by-pixel basis to the one or more videostreams to form the clear rectangles in the composite video output,including for each said video stream: determining when clear rectangleprocessing is enabled for the respective said video stream, wherein theclear rectangle processing is enabled when a z-depth value associatedwith the respective said video stream is greater than zero; and when theclear rectangle processing is enabled, performing clear rectangleprocessing for the respective said video stream by directing the GPU toapply the texture.
 16. The game console as recited in claim 15, whereindirecting the graphics processing unit (GPU) to apply the texture whenthe clear rectangle processing is enabled for the respective said videostream comprises for each said pixel instructing the GPU to: determinewhen a corresponding lookup value referenced from the texture is lessthan or equal to the z-depth value associated with the respective saidvideo stream; and when the lookup value is less than or equal to thez-depth value associated with the respective said video stream, set thepixel to appear transparent in the composite video output.
 17. The gameconsole as recited in claim 15, wherein causing the graphics processingunit (GPU) to apply the texture includes, for each said video stream:when the clear rectangle processing is not enabled, bypassing the clearrectangle processing for the respective said video stream.
 18. The gameconsole as recited in claim 15, wherein the texture is configured as abit-map that includes: for each byte in the texture that does notcorrespond to an area where the one or more clear rectangles aredefined, a sentinel value; and for each byte in the texture thatcorresponds to an area where the one or more clear rectangles aredefined; a z-depth value corresponding to a lowest z-depth of the one ormore clear rectangles that overlap the byte.
 19. The game console asrecited in claim 15 further comprising obtaining data defining the oneor more clear rectangles that is communicated as attributes in a mainvideo stream for the composite video output.
 20. The method as recitedin claim 15 further comprising: monitoring to detect a change in thedata defining the one or more clear rectangles; when the change isdetected, updating the texture to represent the union of one or moreclear rectangles as changed; and applying the updated texture to includethe one or more clear rectangles as changed in the composite output.